This paper concerns the asymmetry in mean axial velocity distributions for the flow through an axisymmetric sudden expansion of a viscoelastic, shear-thinning aqueous solution of a polyacrylamide (PAA). The asymmetry manifests itself as an azimuthal variation in the length of the recirculation region of the separated flow downstream of the expansion inlet. For water, the flow is found to be axisymmetric. The asymmetry for the PAA flow, which remained unchanged despite alterations to the flow facility, is attributed to the high viscoelasticity of the polymer solution. The conclusion is drawn that the asymmetry is a purely physical feature of such a flow, and not the product of upstream or downstream flow conditions deriving from the flow facility, or the result of geometrical imperfections in the axisymmetric sudden expansion set-up. (C) 2004 Elsevier B.V. All rights reserved.